Carbon chain backbone polymers having amino and carboxyl groups attached thereto



United States Patent Int. Cl. C08f 27/08 US. Cl. 26078.5 9 Claims ABSTRACT OF THE DISCLOSURE New water soluble polymers, useful as silver halide emulsion peptizers comprise recurring units having the structure wherein Z is a divalent organic radical, A and B are selected from amino and carboxyl and the ratio of amino to carboxyl is in the range from 1:5 to 1:125 and not more than one of A and B is amino in any one such unit.

This invention relates to silver halide dispersions, and more particularly to the method of preparing silver halide dispersions which involves precipitating silver halide in the presence of certain peptizers.

This is a division of our copending application Ser. No. 391,787, filed Aug. 24, 1964, now Pat. No. 3,392,025.

It is well known that the first step in the preparation of photographic emulsions involves the peptization of silver halides formed by a double decomposition reaction of soluble silver salts and alkali halide salts, either in the presence or the absence of ammonia. Effective peptizat on (1) prevents the insoluble silver halides from precipitating in the form of coarse crystals, which, because of excessive graininess, would be useless in photographic emulsion layers; and (2) prevents clumping and aggregation of the emulsion crystals, thus preventing gross irregularities and the occurrence of infectious development in the developed photographic emulsion layers. A further requirement of eifective peptization is the proper growth of the silver halide emulsion crystals during preparation of the emulsion since the size distributions resulting from this growth have a decisive influence on basic sensitometric properties such as speed, contrast, graininess and acutance.

While gelatin is a satisfactory peptizer, its use has a number of inherent disadvantages. As a naturally occurring material, it is rather sensitive to bacterial attack and its uniformity is questionable due to the variety of sources from which it is obtained. The compatibility of gelatin with other polymeric vehicles which may provide coatings having superior physical properties is also limited, In addition, it is desirable to be able to obtain emulsion crystals which have photographically significant differences in crystal structure and size distribution as compared to those obtained when gelatin is employed.

Many of the polymers which have heretofore been suggested as peptizers for silver halide have not functioned satisfactorily. In many instances, they have not produced effective peptization, which results in clumping and aggregation of the emulsion grains. In other instances, for example, with poly(vinyl alcohol) or polyvinylpyrrolidone, restraint of grain growth by the peptizer has rendered it impossible to obtain sufficiently large, well shaped 3,511,818 Patented May 12, 1970 emulsion crystals having satisfactory photographic characteristics.

One object of our invention is to provide a method for the preparation of silver halid dispersions. Another object of our invention is to provide a method for preparing silver halides which features the precipitation of silver halides in the presence of certain polymeric peptizers. A further object of our invention is to provide silver halide crystals differing photographically in irregularities and size distributions from silver halid crystals obtained when gelatin is employed as peptizer. Another object of our invention is to provide novel polymers. Other objects of our invention will appear herein.

We have discovered new and highly useful polymers having a carbon chain backbone and featuring a pluarlity of amino and carboxyl groups attached directly to separate, adjacent carbon atoms in the polymer backbone. We have found that these polymers, having as the critical feature adjacent carbon atoms substituted with amino and carboxyl groups, are highly useful peptizers for silver halide salts.

A particularly useful class of polymers in accordance with our invention comprises the following repeating units:

wherein A and B are selected from the group consisting of amino and carboxyl, the ratio of amino groups to carboxyl groups in the polymer is from 1.0:5.0 to l.0:1.25; and in each repeating unit, not more than one of A and B is an amino group; and Z is a divalent organic radical, such as, ethylene or substituted ethylene radicals wherein one or more of the hydrogen atoms is rep-laced with one of the following groups: hydroxyl; alkyl, such as methyl or ethyl; or aryl, such as phenyl. These polymers may be prepared by cppolymerizing maleic anhydride with any of the polymerizable polyolefin (e.g., C=CH), groups referred to in Re. 23,514 of Voss et al., US. Pat. 2,047,398 (1936), and selectively converting anhydride groups in the copolymer to amino and carboxyl groups so that no more than one amino group is present in each repeating unit. Not all the anhydride groups need be converted to amino and carboxyl groups. Also, other substituents in place of amino and carboxyl groups (as A and B in the above formula) may be present in minor proportions so long as such substituents do not adversely affect the peptizing qualities of the polymer.

A preferred polymer in accordance with our invention contains the following repeating unit:

wherein A and B are selected from the group consisting of amino and carboxyl, the ratio of amino groups to carboxyl groups in the polymer being from 1.0:5.0 to 1.0: 1.25, and, in each repeating unit, not more than one of A and B is an amino group.

The repeating units defined herein may be arranged in random fashion in the present polymers. For example, the repeating units may be attached to one another in a head-to-head or tail-to-tail manner.

We have found that the above copolymers are particularly effective peptizers in that they promote a very desi'rable type of emulsion crystal grain growth. Thus, the use of the subject copolymers as peptizers results in tabular octahedral grains in neutral emulsions, These grains are of sufficiently large size to provide proper photographic sensitivity. The grain size distribution of the silver halide crystals obtained when peptized in accordance with the invention is distinctively different from that of similarly prepared emulsions which are peptized by gelatin. This is demonstrated by the relationship between the mean grain area of the silver halide obtained and a function known to those familiar with the art as the sigma function, which is a measure of the width of the grain size distribution curve.

The polymeric peptizers of the invention are also usefiul in the preparation of ammo-niacal emulsions. The emulsion grains obtained are of cubic crystalline structure, and have a sufiiciently large size to possess the required photographic sensitivity. Ammoniacal emulsions of unusually high silver halide concentration may be prepared with the polymeric peptizers of the invention without the occurrence of certain deposits or sedimentation which may occur during the preparation of equally high concentrations of silver halide when gelatin is used as peptizer.

We have fiurther found that the size of the silver halide grain can be regulated to some extent by changes in the ratio of amino groups to carboxyl groups in the polymeric peptizers of the invention. Changes in the aminoto-oarboxyl ratio of the polymers employed in the invention result in morphological characteristic changes in the grains, and in changes in the rate of solution of silver halide crystals. In addition, distinct changes in the rate of physical development with a constant silver ion concentration at an efiective catalytic surface are observed if the amino-to-carboxyl ratio in the polymers is varied.

Our invention will be fiuIther illustrated by Examples 1-12.

EXAMPLE 1 Copoly(ethyle-ne B-aminocrylic acid/ ethylene maleic acid), amino-carboxyl ratio of 1.0 to 3.0

A solution of 100 g. of low-molecular-weight copoly (ethylene maleic anhydride) in 800 ml. of concentrated sulfuric acid was placed in a five-liter 3-neck flask fitted with a stirrer, a nitrogen inlet, a thermometer, and a drying tube. The flask was flushed with nitrogen, and sodium azide (46.5 g.) was introduced at such a rate that the temperature remained between 40 and 48 C., with external cooling as necessary. When the sodium azide was completely added and the temperature no longer rose, the solution was heated to 95 C. for two hours. Ligroin added to the solution controls roaming and facilitates stirring. The solution was allowed to cool slowly, overnight, and the polymer precipitated by pouring, in a thin stream, into vigorously stirred acetone. The finely divided precipitate was washed well with acetone and dried.

The polymer was dissolved in 800 ml. of water and the solution diluted to two liters. The polymer was reprecipitated by raising the pH to the isoelectric point (approximately pH 2.4). The polymer was washed well with water and then acetone and then dried. The yield was 78 g.

Analysis (percent) .-C, 45.5; H, 6.9; N, 5.3; Na, 3.

A neutral emulsion was prepared in the following manner. An aqueous solution ml.) of 3.82 g. of silver nitrate was added over a period of 30 minutes to 30 ml. of an aqueous solution containing 3.275 g. of potassium bromide, 0.1 g. of potassium iodide, and 1.0 g. of the copoly(ethylene {E-aminoacrylic acid/ethylene maleic acid). The reaction mixture was kept at 70 C. and stirred continuously. After complete addition of the silver nitrate, the reaction mixture was stirred continuously for an additional ten minutes while the temperature was held at 70 C. The resultant emulsion showed excellent stability and consisted of well dispersed tabular octahedral grains including many triangular shapes with straight edges and sharp corners. The diameters of these grains were in the range 0.33-3.26 microns, the mean grain area was 0.996 square micron, the width of the size distribution curve, expressed in terms of the fiunction known to those skilled in the art as the sigma function corresponded to a value of sigma equal to 1.634 square microns and the number of dislocations per emulsion grain, as determined by well known methods of X-ray analysis, was equal to 8.5. By comparison, a similarly prepared emulsion peptized by gelatin instead of copoly (ethylene fl-aminoacrylic acid/ethylene maleic acid) was found to have a mean grain area of 0.826 square micron, the width of the size distribution curve corresponded to a sigma of 0.807 square micron, and the number of dislocations per grain was equal to 9.1. The coefficient of variation (100 sigma/mean grain area) was 164.1 for the emulsion peptized by copoly(ethylene [i-aminoacrylic acid/ethylene maleic acid) and 97.7 for the emulsion peptized by gelatin.

The fact that the colloid-chemical properties of copoly(ethylene fl-aminoacrylic acid/ ethylene maleic acid) are such as to permit the coagulation of emulsion grains by addition of acid, removal of soluble salts by washing and redispersion in a film-forming vehicle, is evident from the following experimental results.

To an emulsion peptized by the copoly(ethylene ,6- aminoacrylic acid/ethylene maleic acid) polymer there was added a solution of l N sulfuric acid. Dropwise addition to the stirred emulsion was continueduntil the entire emulsion separated out as a coagulum. The soluble salts were then washed out of the coagulated emulsion by repeated addition of water followed by decantation. The coagulum was then dispersed in water containing suflicient sodium hydroxide to raise the pH level above pH 6. The dispersed emulsion grains were then stirred into a 9 percent gelatin solution. The resultant emulsion which contained 4.7 percent silver halide in the form of well dispersed grains and 5 percent gelatin was then coated on a cellulose acetate support after addition of the customary amounts of spreading agent (saponin) and crosslinking agent (formaldehyde). After drying and fixation, the resulting coating was completely clear which shows that satisfactory compatibility between the peptizer, copoly(ethylene ,B-aminoacrylic acid/ethylene maleic acid) and the film-forming vehicle, gelatin, had been attained.

EXAMPLE 2 An ammoniacal emulsion was prepared in the following manner; An aqueous solution (20.0 ml.) containing 3.82 g. silver nitrate and an amount of ammonium hydroxide just sufiicient to redissolve the precipitate formed initially on addition of ammonium hydroxide to the silver nitrate solution, was added with continuous stirring over a period of seconds to 30 ml. of a solution containing 3.14 g. of potassium bromide, 0.1 g. of potassium iodide, and 1.0 g. of copoly(ethylene B-aminoacrylic acid/ethylene maleic acid) (amino-carboxyl ratio of 10:30 described in Example 1). Stirring was continued for an additional 39-minute period. The temperature of the reaction mixture during addition and subsequent stirring was held at 45 C. The resultant emulsion showed excellent stability and consisted of predominantly cubic grains with diameters in the range 0.50-1.76 microns. The mean grain area of this emulsion was 1.581 square microns, the width of the size distribution curve corresponded to sigma equal to 0.61 square micron, and the number of dislocations per grain was equal to 9.4. By comparison, a similarly prepared emulsion for which gelatin was used as the peptizer, had a mean grain area of 1.048 square microns, the width of the size distribution curve corresponded to sigma equal to 0.464 square micron, the number of dislocations per grain was 6.2. The coefficient of variation, as defined in Example 1, was 38.7 for the emulsion peptized by copoly(ethylene fiaminoacrylic acid/ethylene maleic acid) and 44.2 for the emulsion peptized by gelatin.

EXAMPLE 3 An aqueous solution (20.0 ml.) containing 8.495 g. silver nitrate and sufficient ammonium hydroxide to just dissolve the precipitate formed initially during addition of ammonium hydroxide to the silver nitrate solution, was added with continuous stirring over a period of 85 seconds to 30.0 ml. of a solution containing 6.98 g. potassium bromide, 0.226 g. potassium iodide, and 1.0 g. of copoly (ethylene fl-aminoacrylic acid/ ethylene maleic acid) (amino-carboxyl ratio of 1.0 to 3.0 described in Example 1). Stirring was continued for an additional 39 minutes. Throughout this period, during which the temperature was held at 45 C., the well stabilized silver halide emulsion grains remained entirely in suspension. By contrast, some sedimentation of silver halide emulsion grains was observed under these same conditions if gelatin was used as the peptizer instead of copoly(ethylene ,B-aminoacrylic acid/ ethylene maleic acid).

EXAMPLE 4 Copoly(ethylene ,B-aminoacrylic acid/ethylene maleic acid), amino-carboxyl ratio of 1.0 to 5.0

An ammoniacal emulsion was prepared as described in Example 2, except that the peptizer used was copoly(ethylene B-aminoacrylic acid/ethylene maleic acid) (amino carboxyl ratio of 1.0 to 5.0) described in Example 4. The emulsion obtained showed excellent stability and consisted of cubic grains with diameters in the range 0.59-1.67 microns.

EXAMPLE 6 Copoly( ethylene fl-aminoacrylic acid/ethylene maleic acid), amino-carboxyl ratio of 1.0 to 1.5

The procedure of Example 1 was followed except that intermediate molecular weight copoly( ethylene maleic anhydride) and 62 g. of sodium 'azide were used in the preparation. The isoelectric precipitation occurs at pH 2.1 and the yield was 73 g.

Analysis (percent).C, 44.3; H, 7.1; N, 7.5.

A neutral emulsion was prepared with this peptizer as described in Example 4. The emulsion obtained showed excellent stability and consisted of tabular octahedral grains with diameters in the range 0.5-3.3 microns.

EXAMPLE 7 An ammoniacal emulsion was prepared as described in Example 2 with the medium molecular weight peptizer described in Example 6. The emulsion obtained showed excellent stability and consisted of cubic grains with diameters in the range 0.4-2.8 microns.

EXAMPLE 8 Copoly(ethylene B-aminoacrylic acid/ethylene maleic acid), amino-carboxyl ratio of 1.0 to 1.5

The procedure of Example 1 was followed except that 126 g. of copoly(ethylene maleic anhydride) was used with 78 g. of sodium azide. The isoelectric point was approximately 3.5, and 40 g. of product were collected.

Analysis (percent).C, 47.9; H, 7.1; N, 8.5; NH 8.1.

A neutral emulsion was prepared with this peptizer as described in Example 4. The emulsion obtained showed excellent stability and consisted of tabular octahedral grains with diameters in the range 0.5-4.3 microns.

EXAMPLE 9 An ammoniacal emulsion was prepared as described in Example 2 with the low-molecular-weight peptizer described in Example 8. The emulsion obtained showed excellent stability and consisted of cubic grains with diameters in the range 0.6-1.8 microns.

EXAM PLE 1 0 Copoly(ethylene ,B-aminoacrylic acid/ethylene maleic acid), amino-carboxyl ratio of 1.0 to 1.25

A solution of 126 g. of low-molecular-weight copoly (ethylene maleic anhydride) in 800 ml. of concentrated sulfuric acid was cooled to 8 C. in a five-liter 3-neck flask fitted with a stirrer, thermometer, nitrogen inlet and a drying tube. Sodium azide (97 g.) was'added at such a rate that the temperature remained between 8 and 12 C. After the addition was complete, the solution was held at 8 C. for 16 hours, then allowed to warm. The temperature rose to 40 C. spontaneously. When the temperature started to fall, the solution was heated to C. for two hours, cooled and precipitated by pouring, in a fine stream, into acetone, washed well with acetone and dried.

The polymer was dissolved in 800 ml. of water, diluted to 2 liters, and the pH adjusted to 5.2 at which time the polymer reprecipitated. The product was washed well with water, then acetone and dried. The yield was 65 g.

Analysis (percent).C, 45.1; H, 7.2; N, 8.6; Na, .1.

A neutral emulsion was prepared with this peptizer as described in Example 4. The emulsion obtained showed excellent stability and consisted of tabular octahedral grains with diameters in the range 0.65.5 microns.

EXAMPLE 11 An ammoniacal emulsion was prepared as described in Example 2 with the peptizer described in Example 10. The emulsion obtained showed excellent stability and consisted of cubic grains with diameters in the range 0.3-2.6 microns.

EXAMPLE 12 The different interaction effects, with the surface of silver halide grains and during such development processes as physical development, which may be obtained with copoly (ethylene B-aminoacrylic acid/ethylene maleic acid) polymers of different amino/carboxyl ratios, were indicated by the following experimental results. Using the method described by E. J. Perry, Phot. Sci. Eng., 5, p. 349 (1961), the relative (i.e., compared to gelatin) rate of solution of silver halide sol crystals peptized by a given peptizer in a photographic developer, and the relative rate of physical development at a constant silver ion concentration supplied by a silver ion-thiosulfate complex in the presence of the said peptizers were determined. The results obtained were as follows:

Relative rate of Relative rate of physical developsolution of pepment at a contized silver hastant silver ion Polymer am 1no/ Molecular lide crystals concentration carboxyl ratio welght (gelatin 1.00) (gelatin 1.00)

In the above table, low molecular weight refers to a starting copoly(ethylene maleic anhydride) with a specific viscosity of approximately 0.1, and medium molecular weight refers to the same material with a specific viscosity of about 0.6.

The unexpected nature of our invention is demonstrated by the fact that polymers closely related to those of the invention fail to function as silver halide peptizers, as demonstrated in Examples 13 and 14.

EXAMPLE 13 A neutral emulsion was prepared as described in Example 1 except that the peptizer used was copoly(ethy1ene ammonium maleamate). The emulsion obtained was completely unstable (i.e., the silver halide grains were not peptized, but coagulated).

7 EXAMPLE 14 An ammoniacal emulsion was prepared as described in Example 2, except that the peptizer used was copoly(ethlene ammonium maleamate). The emulsion was completely unstable.

The copolymers useful as peptizers in accordance with )ur invention, may be used in any of the methods previ- )usly described in the art which require the use of a ileptizer in the preparation of silver halide dispersions. The most useful molecular weights of the copolymers employed in accordance with the invention correspond to the molecular weight range of polymers derived from copoly(ethylene maleic anhydride) of specific viscosities ranging from 0.1 to 0.6. However, useful results are obtained with copolymers prepared from materials having specific viscosities of 0.02 to 1.0. The most useful ratio of polymeric peptizer to silver halide during emulsion precipitation extends from approximately 0.07:1 to 0.35: 1. However, this concentration may be varied over a considerable range as desired.

The silver halide grains precipitated in accordance with our invention may be washed and added to various vehicles, such as gelatin or synthetic binders, e.g., polyvinyl alcohol or ethyl acrylate-acrylic acid copolymers, for coating purposes. Any precipitation technique, such as those described in Photographic Emulsions by Wall, 1929, may be employed using the copolymers of the invention.

The silver halide peptizers of the invention are useful in the preparation of printout and direct-print emulsions as well as in emulsions of the developing-out type. The emulsions prepared with these peptizers may contain various silver halides, or combinations thereof, and may be utilized, e.g., in solvent transfer systems and color system such as color films having incorporated-coupler systems and color systems in which the coupler is employed in developer solutions. Emulsions prepared using the subject peptizers may be sensitized with chemical or spectral sensitizers, such as those referred to in U.S. Pat. 3,039,873, columns and 11.

The invention has been described in detail with particular reference to preferred embodiments thereof but it will be understood that variations and modifications can be eficcted within the spirit and scope of the invention as described hereinabove and as defined in the appended claims.

We claim:

1. An interpolymer having a carbon chain backbone and repeating units consisting essentially of amino and carboxyl groups, respectively, directly attached to respective adjacent backbone carbon atoms.

'8 2. A polymer consisting essentially of the following repeating unit:

[CHzCH2-$HCH1 wherein A and B are selected from the group consisting of amino and carboxyl; the ratio of amino groups to carboxyl groups in the polymer is from 1.0150 to 1.0:1.25; and, in each repeating unit, not more than one of A and B is an amino group.

3. The interpolymer of claim 1 wherein the ratio of amino to groups to carboxyl groups is from about 1025.0 to about 1.0: 1.25.

4. A polymer consisting essentially of the following repeating unit:

wherein Z is alkylene or substituted alkylene where one or more of the hydrogen atoms is replaced with a radical selected from the group consisting of hydroxyl, alkyl and aryl, A and B are selected from the group consisting of amino and carboxyl; the ratio of amino groups to carboxyl groups is from 1.0:5.0 to 1.01115; and in each repeating unit, not more than one of A and B is an amino group.

5. Copoly(ethylene fi-aminoacrylic acid/ ethylene maleic acid) having an amino to carboxyl ratio from about 1.0:5.0 to about 1.0:1.25.

6. The polymer of claim 5 having an amino to carboxyl ratio of about 1.0230.

7. The copolymer of claim 5 having an amino to carboxyl ratio of about 1.0:5.0.

8-. The copolymer of claim 5 having an amino to carboXyl ratio of about 1.0:1.5.

9. The copolymer of claim 5 having an amino to carboxyl ratio of about 1.0:1.25.

References Cited UNITED STATES PATENTS 2,957,767 10/1960 Williams 260'78.5 XR

JOSEPH L. SCHOFER, Primary Examiner JOHN KIGHT III, Assistant Examiner U.S. Cl. X.R. 260-78 

